Histology Core: Project Summary/Abstract Koch Institute Members use vertebrate model organisms as a key tool to study the role of known or putative cancer genes in development and tumorigenicity; investigate the mechanisms of tumor initiation, progression and metastasis; evaluate the role of stroma and immune responses in tumorigenesis; and assess the efficacy of drugs, nanomaterials and devices in therapeutic and diagnostic applications. Thus, it is essential that Center Members are able to correctly diagnose developmental and tumor phenotypes, evaluate the underlying molecular events, and accurately and quantitatively assess drug or vaccine delivery, localized tissue response, and overall therapeutic response. The Koch Institute Histology Core is a Shared Resource that provides state- of-the-art histological services to support these studies. This includes assistance and/or training in tissue sectioning, slide preparation, staining and analysis, and access to the consultative services of an internationally recognized Veterinary Pathologist, Dr. Roderick Bronson, for diagnosis of tumor and tissue phenotypes. During the current period, usage of the Histology Core increased from 67% to 77% of Center Members, and included investigators from all three Programs. In response to Center member needs, the Histology Core expanded services and instrumentation. This includes expanded offerings for immunohistochemistry and special stains, and investigator training for independent sectioning. The Core also acquired new digital slide scanning capabilities and quantification software, and made upgrades to existing key instrumentation. Thus, this Shared Resource is essential to the success of the Koch Institute mission. In the upcoming period, The Histology Core is committed to offering a wide range of state-of-the-art histological services to support the research programs of Center Members. Planned initiatives include: working with the Integrated Genomics & Bioinformatics Core to establish methodologies for mapping gene expression at the single cell level within tissues; developing expertise and providing guidance in use of automated AI-driven analysis packages (such as QuPath) for analysis of histological sections; evaluating instrumentation to determine community benefit for fluorescent digital slide scanning; and expanding histology training offerings to include more hands-on workshop opportunities. This shared Core is of exceptional value to the CCSG because Koch Institute Members account for 95% of the Core services usage. Notably, the requested CCSG budget for Year 49 is 6.8% less than the budget in the current period (Year 48).